Third Line of Defence

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Third Line of Defence

• Aims
• Must be able to state the substances involved in
  the third line of immunity.
• Should be able to describe the production and
  differentiation of B and T cells.
• Could be able to outline the role of B and T
  cells.

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The Third Line of Defense

• Specific resistance is a third line of defense.
• Forms the immune response and targets specific
  pathogens.
• Specialized cells of the immune system, called
  lymphocytes are
• B-cells produce specific proteins called
  antibodies, which are produced against specific
  antigens.
• T-cells target pathogens directly.

The 2nd line of defense
The 3rd line of defense
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Third Line of Defense

• There are two main components of the vertebrate
  immune system
• The humoral immune system involves the action of
  B-cells, which produce antibodies. The humoral
  system is associated with serum, the non-cellular
  part of the blood.
• The cell-mediated immune system is associated
  with the production of specialized lymphocytes
  called T-cells.
• The humoral and cell-mediated systems work
  separately and together to protect us from
  disease.

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Cells of the Third Line of Defense

• Two main groups of lymphocytes are involved in
  specific immunity.
• All lymphocytes are produced in the bone marrow.
• Mature in the bone marrow - B lymphocytes or B
  cells.
• Mature in thymus gland - T lymphocytes or T
  cells.
• There are different kinds of B and T cells

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Mast Cell - Secretes hisatmines
phagocytes
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Distinguishing Self

• Achieved through the Major Histocompatibility
  Complex (MHC).
• The MHC cluster of tightly linked genes on
  chromosome 6 in humans.
• Genes code for protein molecules (MHC antigens)
  attached to the surface of body cells.
• The MHC antigens are used by the immune system to
  recognise its own and foreign material.
• Class I MHC antigens located on surface of all
  human cells.
• Class II MHC antigens restricted to macrophages
  and B-cells.

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Antigens

• Antigens foreign substances that cause
  formation of antibodies.
• Antigens include
• Potentially damaging microbes and their toxins.
• Substances such as pollen and flea and dust mite
  feces.
• Blood cell surface proteins.
• The surface proteins of transplanted tissues and
  organs.

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BCells

• B-cells (B-lymphocytes) originate and mature in
  the bone marrow of the long bones (e.g. the
  femur).
• Migrate from the bone marrow to the lymphatic
  organs.
• B-cells defend against
• Bacteria and viruses outside the cell
• Toxins produced by bacteria (free antigens)
• Each B-cell can produce antibodies against only
  one specific antigen.
• A mature B-cell may carry up to 100 000 antibody
  molecules embedded in its surface membrane.

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B-Cells

• Each B-Cell only has one type of antibody
• The body needs to defend itself against millions
  of antigens.
• Only a small number of each corresponding
  antibody.
• The type of antibody is genetically
  predetermined.
• Having a small number of each antibody type
  means, more chance of recognising the antigen.

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Humoral Immunity
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BCell Differentiation

• B-cells differentiate into two kinds of cells
• Memory cellsWhen these encounter the same
  antigen again (even years or decades after the
  initial infection), they rapidly differentiate
  into antibody-producing plasma cells.
• Plasma cellsThese secrete antibodies against
  antigens. Each plasma cell lives for only a few
  days, but can produce about 2000 antibody
  molecules per second.

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After the Antigen has Attached to an
Immunoglobulin

• The selected B-Cell then needs to reproduce
  rapidly so that there is a large number of
  identical cells that can respond to the antigen.
• This is called clonal expansion.
• Cells cloned in this way have exactly the same
  genetic material and immunoglobulins.
• Most of these cells will then differentiate into
  plasma cells

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Antigens and Antibodies
Molecular model
Symbolic model

• Antibodies (immunoglobulins) are proteins made in
  response to antigens.
• Antibodies recognize and bind to antigens.
• Antibodies are highly specific and can help
  destroy antigens.
• Each antibody has at least two sites that can
  bind to an antigen.

Antibody
One of the two binding sites on the antibody
Antigen
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Antibody Structure
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Immunoglobulins

• Although there are over 10 million different
  types of immunoglobulins in our bodies, they
  exist in several classes
• IgM antibodies are usually the first to be
  secreted cause an agglutination of antigens
  (makes easier for phagocytes).
• IgG activate complement proteins,neutralise
  toxins directly.
• IgA neutralise pathogens in the digestive,
  respiratory and reproductive tracts.
• IgE help initiate inflammation after infection.

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Inactivation of Antigens
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Inactivation of Antigens
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Activity

• Complete the activities on pages 155 and 156 in
  Biozone book.

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T-Cells

• T-cells originate from stem cells and mature
  after passing through the thymus gland.
• They respond only to antigenic fragments that
  have been processed and presented bound to the
  MHC by infected cells or macrophages (phagocytic
  cells).
• T-cells defend against
• Intracellular bacteria and viruses.
• Protozoa, fungi, flatworms, and roundworms.
• Cancerous cells and transplanted foreign tissue.

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T-Cell Differentiation

• T-cells can differentiate into four specialized
  types of cell
• Helper T-cell
• Activates cytotoxic T cells andother helper T
  cells.
• Necessary for B-cell activation.
• Suppressor T-cell
• Regulates immune response by turning it off when
  no more antigen is present.
• T-cell for delayed hypersensitivity
• Causes inflammation in allergic reactions and
  rejection of tissue transplants.
• Cytotoxic (Killer) T-cell
• Destroys target cells on contact.

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Cell Mediated Immunity
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Activity

• Complete the activities on pages 153 in Biozone
  book.